A liquid crystal display panel is a panel composed of two glass substrates, whose peripheral edges adhered using an adhesive (sealing agent) while maintaining a gap by particulate spacers between two glass substrates, and liquid crystal is injected into the gap. The liquid crystal display panel used in each display device differs greatly in a display size according to the application. In particular, a liquid crystal display panel for television receiver or monitor is becoming larger year after year, and accompanied therewith, a glass substrate used in the liquid crystal display panel is becoming larger and thinner year after year.
A plurality of the liquid crystal display panel substrates are simultaneously manufactured by dividing a large-sized mother liquid crystal display panel substrate. In such a process that the liquid crystal display panel substrate is manufactured by cutting the large-sized mother liquid crystal display panel substrate, a vacuum suction device is used to suck and convey the liquid crystal display panel substrate between steps of the process. The vacuum suction device provides one or a plurality of suction pads. The liquid crystal display panel substrate is formed by laminating two glass substrates of approximately 0.5 mm to 0.7 mm thin plate. Such liquid crystal display panel substrate bends easily. Thus, each location of the liquid crystal display panel substrate must be sucked and conveyed using a plurality of suction pads when conveying, in particular, the large-sized liquid crystal display panel substrate.
A conventional vacuum suction head will now be explained. The liquid crystal display panel substrate is explained as an example of the object to be sucked in following explanation. FIG. 1 shows a configuration view of a suction pad of conventional example 1 disclosed in patent document 1. The suction pad 51 is configured with a rubber suction disk 51a of semispherical shape, and a suction tube 51b coupled to an upper part of the suction disk 51a. The suction pad 51 is widely used to suck an object to be sucked such as not only the liquid crystal display panel substrate but a plate-shaped molded article made of resin, thin plate made of metal and the like. However, when a liquid crystal display panel substrate is sucked by the suction pad 51 of conventional example 1, a glass surface curves, uneven distribution occurs in a spacer interposed between the glass substrates, there has been a possible that product defect of the liquid crystal display panel substrate occurs as a result of uneven distribution, caused by curvature of glass surfaces, of spacers interposed between the glass substrates.
FIG. 2 is a cross-section view showing a configuration of a suction pad 61 disclosed in the patent document 1. The suction pad 61 is dealt with as conventional example 2. A suction disk 62 is a disk-shaped suction disk made of photosensitive resin material, and a suction port 62c penetrating through in the up and down direction is formed at its central part. A great number of convex parts are arranged on a sucking surface side of the suction disk 62, and a flat surface having the same height as the convex parts is provided at an outer peripheral edge to maintain air tightness. The convex parts are formed by performing photo etching process for the photosensitive resin material (AFP). A reinforcement layer 63 is a layer laminated to prevent the AFP from deforming by external stress. A magnet sheet 64 is a sheet having the same diameter as the suction disk 62. A double-faced adhesive sheet 65 is an adhesive sheet for bonding the magnet sheet 64 and the reinforcement layer 63. Each of these members 63 to 65 provides a hole Q at a position corresponding to the suction port 62c. A holding member 66 10 made of iron is a holding member made of iron having the same outer diameter as the magnet sheet 64. A supporting member 66a for supporting the holding member itself is arranged at the central part of the holding member 66. A suction tube 67 is inserted into the supporting member 66a. The suction tube 67 is connected to a vacuum pump which is not shown.
The suction disk 62 formed in such manner pushes against a flat liquid crystal display panel substrate and performs vacuuming through the suction port 62c. In this manner, the suction pad 61 can made the liquid crystal display panel substrate sucked to the suction disk 62 without deforming. Since the suction disk 62 is composed of a flexible material, a high suction performance is achieved even if the liquid crystal display panel substrate has slight flexure. However, a large flexure is formed at the liquid crystal display panel substrate by the weight of the substrate when conveying the large-sized liquid crystal display panel substrate using the suction pad 51 of conventional example 1 or the suction pad 61 of conventional example 2 described above. The arrangement density of the suction pad must be made high with respect to the liquid crystal display panel substrate to prevent the flexure.
A case of moving the large-sized liquid crystal display panel substrate to next step of the process after mounting the liquid crystal display panel substrate on a working table will be considered. A plurality of suction pads are required to be arranged on a conveying machine at a suitable interval corresponding to a shape of a liquid crystal display panel substrate so that the conveying machine sucks and holds a large-sized liquid crystal display panel substrate at suction pads from a working table. In this case, the suction height of each suction pad must be aligned at a predetermined precision. If undulation is present at a surface of the liquid crystal display panel substrate, vertical line directions of sucking surfaces on the liquid crystal display panel substrate differs each other depending on their locations. Thus, if central axis directions of the plurality of suction pads are all fixed in the same direction, the clearance between the suction pad and the liquid crystal display panel substrate may not be a predetermined value, or may form space thereby causing suction failure.
A suction device in which central axis directions of suction pads (hereinafter referred to as suction disk depending on the document) change with respect to a surface of an object to be sucked, that is, whose suction pads can freely oscillate will be explained as conventional example 3. FIG. 3 is a cross-section view showing a configuration of a vacuum suction pad disclosed in patent document 2. The vacuum suction pad has a pad 72 arranged on a periphery of a suction disk 71, and the suction disk 71 and the pad 72 are held in a freely oscillating manner using a supporting rod 74. An air passage hole 75a coupling to a vacuum pump is formed in the supporting rod 74 having a spherical end, and an air passage hole 75b is also formed in the suction disk 71. And then, a space S surrounded by the suction disk 71 and the pad 72 can be discharged from or charged with air through the air passage hole 75b. A spring 79 is contacted to the air passage hole 75a and a spool valve 77 is inserted. A sensor rod 78 extending to an end face of the pad 72 is attached to an end of the spool valve 77. A center part of a supporting body 73 for holding the suction disk 71 is cut out into a spherical shape to hold the spherical part of the supporting rod 74 in a freely oscillating manner.
When the object to be sucked is contacted to the suction device, the sensor rod 78 contacts the surface of the object to be sucked, and then, the spool valve 77 lifts against the reactive force of the spring 79. At this time, the air flow holes 75a and 75b communicate each other, and air is discharged from the space S by a vacuum pump. The space S is thereby held in a vacuum state.
A vacuum suction device arranged with a great number of suction pads is disclosed in patent document 3 (not shown). This discloses that an object to be sucked is a mother liquid crystal display panel substrate. The vacuum suction device sucks in vacuum and conveys the mother liquid crystal display panel substrate mounted on a working table. The vacuum suction device is characterized in arranging a tilt adjuster so that a large number of suction pads can be adjustable to become parallel to a surface of the mother liquid crystal display panel substrate.
FIG. 4 is a cross-section view showing a configuration of a vacuum suction device 80 in conventional example 4 disclosed in patent document 3. An extended strip 81 extends in a moving direction and a vertical direction of a movement table. A cylinder 82 is attached to the extended strip 81. A horizontal supporting plate 83 is arranged below the extended strip 81, and a suction fixing member 84 is attached further below being parallel to the horizontal supporting plate 83. The cylinder 82 moves the horizontal supporting plate 83 up and down with using two shafts 85 as guiding rods. Four shafts 86 penetrate the horizontal supporting plate 83 fixed to the suction fixing member 84. The balance in a horizontal direction of the suction fixing member 84 is adjusted through the intermediately of a spring 87 by adjusting a nut 88. Further, four tilt adjusters 89 are attached to four corners of the suction fixing member 84. A mother liquid crystal display panel substrate 90 is mounted on a working table 91.
According to such configuration, the distance of the suction fixing member 84 with respect to a surface of the working table 91 can be adjusted for every tilt adjuster 89. A tilt of the suction fixing member 84 is adjusted so as to be horizontal. The suction fixing member 84 has a cavity therein. A plurality of suction pads 92 are attached to a lower surface of the suction fixing member 84. A configuration of the suction pads 92 is the same as that in conventional example 2 shown in FIG. 2.
A method of preliminarily fixing the working table 91 and the plurality of suction pads 92 in parallel will be explained next. The suction fixing member 84 is lowered by driving the cylinder 82 toward the surface of the working table 91. The suction pads 92 are set at a position having 1 to 2 mm clearance from the surface of the working table. Thereafter, a level is arranged on an upper surface of the suction fixing member 84, and lower end positions of tilt adjustment bars 89a at the four tilt adjusters 89 are adjusted so that the suction fixing member 84 becomes horizontal. At this time, the lower end positions of the four tilt adjustment bars 89a are detected using a position detector which is not shown, and stored in a first position memory which is not shown.
The mother liquid crystal display panel substrate 90 to be sucked and conveyed is then mounted on the working table 91. The suction fixing member 84 is positioned by the drive of a motor 89b so that the suction pads 92 are at a height most suitable for sucking and fixing the mother liquid crystal display panel substrate 90. The lower end positions of the four tilt adjustment bars 89a at this point are detected using the position detector and stored in a second position memory which is not shown.
According to such setting, the suction pad 92 is automatically positioned with respect to a new mother liquid crystal display panel substrate 90 each time the mother liquid crystal display panel substrate 90 is conveyed. If a thickness of the mother liquid crystal display panel substrate 90 changes, a value of the second position memory changes based on the relevant value.
Patent Document 1: Japanese Unexamined Patent Publication No. 11-19838
Patent Document 2: Japanese Unexamined Utility Model Publication No. 48-45064
Patent Document 3: International Patent Publication WO 03/049909 A1